There are apparatuses which read signals from the signal recording medium using an optical type pickup apparatus. A CD player is known as one representative among the apparatuses, which reproduces signals from compact discs (CD), which have projections called pits. The reproduced signals correspond to the digital signals formed on the signal face of the CD. In a CD player, it is necessary to perform a focusing controlling operation to control the optical beam in the optical axis direction, the so-called focusing direction, to correctly converge the optical beam produced from the optical type pickup apparatus on the signal face of the disc. It is also necessary to perform a tracking controlling operation to control the optical beam in the radial direction of the disc, the so-called tracking direction, to cause it to follow the signal track on the disc.
A method for controlling the position of the objective lens is necessary for the optical type pickup to perform the focusing control and the tracking control. As in, for example, Japanese Laid-Open Patent application Tokkaisho No. 57-71532 Publication, it is known in the optical type pickup that a lens holder for retaining the objective lens is provided as a bobbin. The focusing coil and the tracking coil are mounted on the lens holder. The lens holder is disposed in a given position in the magnetic field caused by the magnetic field in the electric mechanical transducer. The position of the objective lens retained by the lens holder is controlled with the lens holder being driven in accordance with the control signals flowing (input) into the focusing coil and the tracking coil.
As described in the publication, the optical type pickup was constructed so that the direction of the current flowing into the focusing coil and the direction of the current flowing into the tracking coil may become vertical to each other. Also, the direction of the magnetic flux, caused by the magnetic circuit, and the directions of the respective currents flowing into the focusing coil and the tracking coil may also become vertical to each other. Thus, as the magnetic circuit was required to be constructed so that the magnetic-pole face of the N polarity and the magnetic pole face of the S polarity might oppositely face each other with the focusing coil and the tracking coil being interposed, the yoke coupled to one magnetic-pole face of a magnet, constructing the magnetic circuit, had to be disposed in the space provided within the lens holder. As the optical passage of the optical beam was required on the lens holder to read the signals on the disc, the lens holder became larger, thus preventing the optical type pickup from becoming smaller.
Also, normally in an optical type pickup apparatus, where the objective lens is disposed with the lens holder, the tracking coil and the focusing coil are wound on the lens holder to feed the control signals to the tracking coil and the focusing coil to perform the tracking control and the focusing control. Thus, the optical type pickup apparatus was required to support the lens holder so that it could freely move in the tracking direction and the focusing direction in accordance with the input control signals.
As shown in FIG. 1 of Japanese Laid-Open Patent Application Tokkaisho No. 57-127934 Publication, an optical type pickup apparatus as described hereinabove, a method of using a support member composed of a viscometric elastic member was known to support the driven member as the lens holer. As the support member was elastic, torsion was caused by the force to be applied in the axial direction of the support member so that the posture of the lens holder could not be retained properly.
Also, a support apparatus as a cantilever type was conventionally known where, for example, four steel wires were disposed in parallel. One end of the steel wire was secured to the frame and the other end thereof was secured to the lens holder. The support apparatus, which is a cantilever type, may use a steel wire as the steel member which did not have elasticity in the axial direction. The support apparatus had an advantage in that the posture of the lens holder could be kept with respect to the force to be applied in the axial direction.
However, the cantilever type of support apparatus using the steel material (wire) had to retain the weight of the lens holder only with the wire. Thus, the wire had to be made thicker to increase the strength so that stiffness became larger, resonance frequency became higher, and thus the wire is vulnerable to vibration. Due to the unbalance of the driving force, the support position of the lens holder, during the tracking controlling or the focusing controlling, was concentrated on a single side of the lens holder. Thus, a rolling operation (rolling) was caused so that the correct posture could not be retained.